Path searching method and device

ABSTRACT

A path searching apparatus which is used in a base station apparatus according to the CDMA (Code Division Multiple Access) systems for increasing the accuracy for path detection depending on the number of communication channels to be processed. The path searching apparatus has a path searcher for generating a delay profile through to a path searching process composed of a plurality of processing units, an interpolation information storage for storing interpolation information indicative of whether an interpolation process for reducing a chip interval is to be performed or not before and after each of the processing units, an interpolation position processing control for enabling the path searcher to perform an interpolation process before and after each of the processing units based on the interpolation information stored in the interpolation information storage according to the number of the communication channels to be processed, and a path detector for detecting a reception path based on the delay profile generated by the path searcher.

TECHNICAL FIELD

The present invention relates to a method of and an apparatus forsearching for a certain path from a plurality of paths by interpolatinga reception signal in radio communications. More particularly, thepresent invention relates to a method of and an apparatus for pathsearch to remove the effect of multipath fading by interpolating areception signal of a code division multiple access (CDMA) system, forexample.

BACKGROUND ART

In recent years, mobile communication systems such as portable telephonesystems have been in widespread use as multifunctional inexpensivecommunication systems because of the advanced semiconductor technologyand mobile communication technology. Multiplexing schemes that haveheretofore been available for mobile communication systems, typicallyportable telephone systems, include frequency division multiple access(FDMA) and time division multiple access (TDMA) schemes. Recently, therehas been put to use a CDMA mobile communication system, which is capableof multiplexing more channels in the same frequency range than the abovemultiplexing schemes, as a next-generation mobile communicationtechnology.

According to the CDMA mobile communication system, a transmission signalis spread at the transmission side into a wide frequency range using aninherent spreading code that is allotted to the signal, and a receptionsignal is despread (demodulated) using the same spreading code at thereception side. As a result, it is possible to mix a plurality ofchannels spread by respective inherent spreading codes from a pluralityof users in one frequency band.

In a mobile communication system, a transmission signal from thetransmission side is generally subject to multipath fading in itspropagation. Specifically, a reception side receives a combination ofwaves propagating over different paths and received at different timeinstants, i.e., direct and reflected waves propagating through differentpaths. The effect of such multipath fading needs to be removed in orderto improve the reception quality. A path search device in a base stationapparatus of a mobile communication system interpolates a receptionsignal to increase the accuracy of path detection to detect a receivedwave over a certain path for thereby efficiently removing the effect ofmultipath fading.

For example, a path search device in a base station apparatus of a CDMAmobile communication system is constituted as a searcher of the basestation apparatus. The searcher interpolates the reception signal toreduce chip intervals of the reception signal to detect a reception timeinstant at which a signal is to be received. The base station apparatusalso has fingers associated with the searchers for extracting certainpaths from the reception signal based on the reception time instantdetected by the searchers and performing RAKE combining.

FIG. 1 schematically shows an arrangement of a conventional base stationapparatus in a CDMA mobile communication system. Here, only thereception function portion of the base station apparatus is illustrated.

Base station apparatus 10 comprises antenna 11 for receiving atransmission signal that has been spread according to CDMA scheme from amobile terminal on a transmission side, not shown, receiver 12 having aninterface function for a signal received by antenna 11 and demodulatingthe reception signal, parameter manager 13 for allotting spreading codesto respective communication channels (CHs) and managing the spreadingcodes, N searchers 14 ₁ to 14 _(N) and N fingers 15 ₁ to 15 _(N) forbeing allotted to the respective communication channels by parametermanager 13, and reception processor 16 for performing a predeterminedreception process on the reception signal over certain paths extractedby fingers 15 ₁ to 15 _(N). Searchers 14 ₁ to 14 _(N) and fingers 15 ₁to 15N are associated with each other in one-to-one correspondence. Nsearchers 14 ₁ to 14 _(N) are structurally identical to each other, andN fingers 15 ₁ to 15 _(N) are also structurally identical to each other.First searcher 14 ₁ interpolates reception signal received by receiver12 to detect a certain reception time instant, and indicates thedetected reception time instant to first finger 15 ₁ that is associatedwith first searcher 14 ₁. First finger 15 ₁ extracts a certain pathrepresenting the reception time instant indicated by first searcher 14 ₁from the reception signal received by receiver 12, and despreads thesignal propagated over the path. Thereafter, first finger 15 ₁ performsRAKE combining on signals of a plurality of paths for which receptiontime instants are similarly indicated, and outputs the combined signalto reception processor 16. Other searchers 14 ₂ to 14 _(N) also operatein the same manner as with first searcher 14 ₁.

In the mobile communication system including the base station apparatuswith the above-described configuration, a non-illustrated mobileterminal on the transmission side sends a framed transmission signalhaving a plurality of time slots. To each of the time slots, there isadded a pilot signal at its leading position which represents a fixedpattern known to both transmission and reception sides. The pilot signalis subjected to quadrature modulation together with the transmissiondata. After the quadrature modulation, the pilot signal and thetransmission data are spectrum-spread using an inherent spread code forthe communication channel. The transmission signal thus spread usingrespective inherent spreading codes in the CDMA system are received byantenna 11 of the base station apparatus. Receiver 12 performs signalinterface conversion such as amplification and quadrature demodulation,e.g., multiplies a reception signal received by antenna 11 by areference frequency which is generated by a reference frequencygenerator, not shown, with a multiplier, not shown, thereby convertingthe reception signal into a baseband signal.

Parameter manager 13 is arranged to allot a finger and a searcher toeach of communication channels included in the reception signal. Forexample, parameter manager 13 allots unused fingers and searchers,successively from first finger 15 ₁ and first searcher 14 ₁ torespective communication channels. Then, parameter manager 13 indicatescode generating information for generating corresponding spreading codesto the allotted fingers and searchers, which generate spreading codesthat are associated with the code generating information indicatedthereto.

Demodulated signal that is demodulated in receiver 12 is supplied to thesearchers and fingers that have been allotted by parameter manager 13.

Each searcher interpolates sampling points in order to reduce chipintervals of the reception signal, and generates a delay profile basedon the pilot signals added to the leading positions of the time slots ofthe interpolated signal. In the delay profile, the power values ofreception signal components which are orthogonal to each other that aredemodulated by receiver 12 are calculated for respective delay times inorder to indicate a temporal change of reception time instants of thedemodulated signal due to multipath fading. Usually, the power valuescalculated for the respective delay times on the delay profile representpeaks on a plurality of different propagating paths due to the effect ofthe multipath fading. Each searcher then detects peaks in excess of apredetermined threshold, and indicates delay times corresponding to thedetected peaks to the finger associated therewith. The finger thusnotified then extracts path of the received wave corresponding to theindicated delay time from the demodulated signal produced by receiver12. The extracted paths are then RAKE-combined and then processed byreception processor 16.

Since the accuracy with which to detect paths depends upon thesearchers, the searchers determine the reception quality of the basestation apparatus. The arrangement of searchers will be described below.Because searchers 14 ₁ to 14 _(N) are structurally identical to eachother, the arrangement of first searcher 14 ₁ will be described. FIG. 2shows the arrangement of first searcher 14 ₁.

First searcher 14 ₁ comprises first interpolating filter 20 forinterpolating sampling points of the demodulated signal from receiver 12to reduce chip intervals thereof, correlation value calculator 21 forcalculating a correlation value of data interpolated by firstinterpolating filter 20, in-phase adder 22 and power adder 23 forgenerating a delay profile based on the calculated correlation value,second interpolating filter 24 for further reducing chip intervals ofthe generated delay profile, path controller 25 for indicating paths tobe extracted to a corresponding finger, and code generator 26 forgenerating a spreading code for the calculation of the correlationvalue.

The interpolating filters will be described below. FIG. 3 shows astructure of first interpolating filter 20. It is assumed that theoversampling number is “2” and the tap length is “4”. Firstinterpolating filter 20 has first to seventh delay elements 27 ₁ to 27₇, first to eighth multipliers 28 ₁ to 28 ₈, and adder 29. First toseventh delay elements 27 ₁ to 27 ₇ are connected in series with eachother. Input signals applied to first to seventh delay elements 27 ₁ to27 ₇ and an output signal from seventh delay element 27 ₇ are suppliedrespectively to first to eighth multipliers 28 ₁ to 28 ₈. To first toeighth multipliers 28 ₁ to 28 ₈, there are applied respectivepredetermined filter coefficients C₋₄, C₋₃, C₋₂, C₋₁, C₁, C₂, C₃, C₄,which are multiplied by the input signals applied to respective delayelements and the output signal from seventh delay element 27 ₇. Assumingi=1 to 4, the filter coefficients C_(-i) and C_(i) are equal to eachother. Products produced by respective multipliers 28 ₁–28 ₈ are addedto each other by adder 29, which is then supplied as output signal 31 ofinterpolating filter 20 to the outside.

First interpolating filter 20 thus constructed can determine aninterpolation point using values of the input signal at four pointsbefore and after input signal 30. As input signal 30 are more delayed,the input signal is shifted and interpolating points are successivelydetermined. The interpolated serial interpolating data are supplied asoutput signal 31 to correlation value calculator 21 (FIG. 2).

Referring back to FIG. 2, based on the code generating informationcorresponding to the communication channel allotted from the parametermanager to first searcher 14 ₁, code generator 26 generates a spreadingcode corresponding to the communication channel. Correlation valuecalculator 21 detects the pilot signals added to the leading positionsof respective time slots from the interpolation data interpolated byfirst interpolating filter 20 shown in FIG. 3, and generates idealreception signals by spreading pre-recognized pilot signals with thespreading code generated by code generator 26. Correlation valuecalculator 21 then multiplies the detected pilot signals and thegenerated ideal reception signals to calculate correlation valuesthereby performing quadrature demodulation on the pilot signals. As aresult of the quadrature demodulation, the pilot signals are outputtedas I (In-Phase) signals and Q (Quadrature-Phase) signals which areorthogonal to each other. In-phase adder 22 performs a certain number ofin-phase additions “I+I”, and “Q+Q” on the I signal component and the Qsignal component from correlation value calculator 21.

Power adder 23 performs a certain number of power additions “I²+Q²” onthe output from in-phase adder 22. Second interpolating filter 24, whichis of the same structure as first interpolating filter 20, interpolatesadded power data in order to further reduce chip intervals. Pathcontroller 25 refers to a delay profile in which reception signalsinterpolated and expressed as power values by second interpolatingfilter 24 are arranged with respect to respective delay times, detectspeaks in excess of a predetermined threshold value, and indicates delaytimes corresponding to the detected peaks to first finger 15 ₁.

First searcher 14 ₁ thus arranged has a central processing unit (CPU),not shown, which can execute various control processes based on acontrol program stored in a given storage device such as a read-onlymemory (ROM) or the like.

FIG. 4 shows the content of the processing of the control program whichis stored in such a given storage device. In first searcher 14 ₁,modulated signals from receiver 12 are interpolated at “½” chipintervals, for example, in first interpolating filter 20 as step S33. Todo so, the oversampling number in the interpolating filter of theconstitution shown in FIG. 3 may be set to “2”. Then, in step S44,respective correlation values are calculated in correlation valuecalculator 21 for pilot signals which are of predetermined fixedpatterns added to the leading positions of time slots, of the I and Qsignals that have been interpolated at the “½” chip intervals. Becausethe pilot signals are of predetermined fixed patterns, it is possible toaccurately determine ideal waveforms at the reception side. Incorrelation value calculator 21 calculates, correlation values withrespect to ideal reception signals produced by spreading pre-recognizedpilot signals with spreading codes generated by code generator 26 arecalculated in the respective time slots of a received frame. A highercorrelation value represents that the waveform of the pilot signal atthe leading position of each time slot is closer to an ideal waveform,indicating a better reception sensitivity.

The calculated correlation values are added a given number of times Nfor I and Q signal components by in-phase adder 22, thus removing noisecomponents contained in the I and Q signals, in step S35. The greaterthe number of in-phase additions, the smaller the noise components ofthe I and Q signal components.

The result of the in-phase additions is then added for power a givennumber of times M by the power adder 23 in step S36. The power valuesare thus averaged with respect to time, preventing paths from beingdetected with wrong power values due to instantaneous noise.

The values of in-phase additions are further interpolated at “¼” chipintervals, for example, by second interpolating filter 24 in step S37.As described above, second interpolating filter 24 is of a structuresimilar to first interpolating filter 20.

The calculated power values represent a delay profile on a temporal axiswhich indicates reception signals that are converted into power valuesfor respective delay times. Path controller 25 detects peaks in excessof a predetermined threshold, of the power values for respective delaytimes. Path controller 25 then indicates the delay times correspondingto the peaks in excess of the threshold to first finger 15 ₁ in stepS38.

As described above, each of the searchers including first finger 15 ₁performs an interpolation process to increase the number of samplingpoints for increasing the accuracy of a subsequent process in order toachieve a higher accuracy for path detection.

In the conventional path searching apparatus described above, theaccuracy for path detection is increased by the interpolation by firstand second interpolating filters 20, 24 in steps S33, S37. The number ofinterpolating operations is greater if they are performed beforecorrelation values are calculated and in-phase additions are made thanif they are performed before correlation values are calculated and afterpower additions are performed in searchers 14 ₁ to 14 _(N) as in stepsS33, S37, resulting in an increased accuracy for path detection.Presently, however, because of a limitation posed on the calculationamount allowed by the searchers, interpolating operations are performedbefore correlation values are calculated and after power additions aremade as in steps S33, S37. The number of interpolating operationsincreases and the amount of subsequent processing increases due to theinterpolating operations also increases. As a result, there is atrade-off between the accuracy for path detection and the amount ofprocessing.

The calculation processing in searchers 14 ₁ to 14 _(N) varies with timedepending on the number of communication channels to be processed.Heretofore, however, interpolating operations have fixedly beenperformed before correlation values are calculated and after poweradditions are performed, irrespective of the number of communicationchannels to be processed. Specifically, if the number of communicationchannels to be processed by the searchers is small, there is a situationwhere an extra amount of calculation is available for performinginterpolating operations before correlation values are calculated andin-phase additions are made. Heretofore, since interpolating operationsare performed in a fixed sequence, the number of interpolatingoperations is small, making it impossible to increase the accuracy forpath detection.

Japanese laid-open patent publication No. Hei 10-190522 (JP, A,10190522) discloses a technique with respect to a path searchingapparatus for using a matched filter to select signals, greater than apredetermined threshold, of all multipath signals in a multipath searchrange and perform a RAKE combining on the selected signals for therebycombining all multipaths, and excluding the RAKE combining in chipphases where the signal level is low according to a threshold judgmentusing an average delay profile. According to the disclosed technique, itis also necessary to carry out processing operations in the range of allsearched paths at all times regardless of the number of communicationchannels to be processed. The disclosed path searching apparatus isusually optimized to maintain a certain level of accuracy in a maximumallowable range. However, it is desirable for the path searchingapparatus to have as good an accuracy for path detection as possible ifthe number of communication channels is small and an extra amount ofcalculation is available.

DISCLOSURE OF THE INVENTION

It is a first object of the present invention to provide a pathsearching method of increasing the accuracy for path detection dependingon the number of communication channels to be processed.

It is a second object of the present invention to provide a pathsearching apparatus for increasing the accuracy for path detectiondepending on the number of communication channels to be processed.

The first object can be achieved by a method of searching for a path,comprising:

-   -   a first interpolating step of interpolating a demodulated signal        to generate a first interpolated signal;    -   a first selecting step of generating a first selected signal by        alternatively selecting the first interpolated signal or the        demodulated signal based on interpolation information, said        interpolation information indicating whether an interpolation        process for reducing a chip interval is to be performed or not        between processes for generating a delay profile which indicates        a temporal change of reception time instants of the demodulated        signal due to multipath fading;    -   a correlation value calculating step of calculating a        correlation value between a pilot pattern which is included in        the first selected signal and has a predetermined fixed pattern        and a predetermined expected value;    -   a second interpolating step of interpolating the correlation        value calculated in the correlation value calculating step to        generate a second interpolated signal;    -   a second selecting step of generating a second selected signal        by alternatively selecting the second interpolated signal and        the correlation value based on the interpolation information;    -   an in-phase adding step of adding in-phase components of the        second selected signal for a predetermined number of times;    -   a third interpolating step of interpolating an in-phase addition        sum calculated in the in-phase adding step to generate a third        interpolated signal;    -   a third selecting step of generating a third selected signal by        alternatively selecting the third interpolated signal or the        in-phase addition sum based on the interpolation information;    -   a power adding step of adding power values calculated from        signal components of the third selected signal for a        predetermined number of times;    -   a fourth interpolating step of interpolating a power addition        sum calculated in the power adding step to generate a fourth        interpolated signal;    -   a fourth selecting step of generating a fourth selected signal        by alternatively selecting the fourth interpolated signal or the        power addition sum based on the interpolation information; and    -   a path detecting step of detecting a path in excess of a        predetermined threshold based on the fourth selected signal.

The second object can be achieved by an apparatus for searching for apath, comprising:

-   -   path searching means for generating a delay profile based on a        pilot signal which is included in each time slot and has a fixed        pattern, according to a path searching process composed of a        plurality of processing units, the delay profile indicating a        temporal change of reception time instants due to multipath        fading of a demodulated signal;    -   interpolation information storage means for storing        interpolation information indicative of whether an interpolation        process for reducing a chip interval is to be performed or not        before and after each of the processing units;    -   interpolation position processing control means for enabling the        path searching means to perform an interpolation process before        and after each of the processing units based on the        interpolation information; and    -   path detecting means for detecting a reception path based on the        delay profile generated by the path searching means.

The second object can also be accomplished by an apparatus for searchingfor a path, comprising:

-   -   interpolation information storage means for storing        interpolation information indicative of whether an interpolation        process for reducing a chip interval between processes for        generating a delay profile is to be performed or not, the delay        profile indicating a temporal change of reception time instants        of a demodulated signal due to multipath fading;    -   first interpolating means for interpolating the demodulated        signal to generate a first interpolated signal;    -   first selecting means for generating a first selected signal by        alternatively selecting the first interpolated signal or the        demodulated signal based on the interpolation information;    -   correlation value calculating means for calculating a        correlation value between a pilot pattern which is included in        the first selected signal and has a predetermined fixed pattern        and a predetermined expected value;    -   second interpolating means for interpolating the corrected value        calculated by the correlation value calculating means to        generate a second interpolated signal;    -   second selecting means for generating a second selected signal        by alternatively selecting the second interpolated signal and        the correlation value based on the interpolation information;    -   in-phase adding means for adding in-phase components of the        second selected signal for a predetermined number of times;    -   third interpolating means for interpolating an in-phase addition        sum calculated by the in-phase adding means to generate a third        interpolated signal;    -   third selecting means for generating a third selected signal by        alternatively selecting the third interpolated signal or the        in-phase addition sum based on the interpolation information;    -   power adding means for adding power values calculated from        signal components of the third selected signal for a        predetermined number of times;    -   fourth interpolating means for interpolating a power addition        sum calculated in the power adding means to generate a fourth        interpolated signal;    -   fourth selecting means for generating a fourth selected signal        by alternatively selecting the fourth interpolated signal or the        power addition sum based on the interpolation information; and    -   path detecting means for detecting a path in excess of a        predetermined threshold based on the fourth selected signal.

In the present invention, the demodulated signal is typically a signalproduced by converting a reception signal of a CDMA (Code DivisionMultiple Access) system into a baseband signal and processing thebaseband signal by way of quadrature demodulation. The interpolationinformation may preferably comprise information indicative of whether aninterpolation process is to be performed or not depending on the numberof communication channels to be processed, or information indicative ofwhether an interpolation process is to be performed or not depending onthe reception quality measured in each communication channel of thedemodulated signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an arrangement of a conventional basestation apparatus in a mobile communication system of CDMA scheme;

FIG. 2 is a block diagram showing an arrangement of an essential portionof a searcher in the base station apparatus shown in FIG. 1;

FIG. 3 is a block diagram showing an arrangement of an essential portionof an interpolating filter;

FIG. 4 is a flowchart schematically showing a processing sequencecarried out by the searcher shown in FIG. 2;

FIG. 5 is a block diagram schematically showing an arrangement of a basestation apparatus in a mobile communication system of CDMA scheme whichincorporates a path searching apparatus according to a first embodimentof the present invention;

FIG. 6 is a block diagram showing an arrangement of an essential portionof the path searching apparatus according to the first embodiment of thepresent invention;

FIG. 7 is a diagram showing an example of interpolation informationstored in an interpolation information memory;

FIG. 8 is a diagram showing an example of a format structure ofinterpolation position indicating information in the path searchingapparatus according to the first embodiment;

FIG. 9 is a flowchart schematically showing a processing sequencecarried out by a searcher in the path searching apparatus according tothe first embodiment;

FIG. 10 is a block diagram showing an arrangement of an essentialportion of a path searching apparatus according to a second embodimentof the present invention; and

FIG. 11 is a flowchart schematically showing a processing sequencecarried out by a searcher in the path searching apparatus according tothe second embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be described indetail below.

FIRST EMBODIMENT

An arrangement of a base station apparatus in a mobile communicationsystem of CDMA scheme to which a path searching apparatus according to afirst embodiment of the present invention is applied is schematicallyshown in FIG. 5. Here, only a receiving function section of the basestation apparatus is illustrated. Those components shown in FIG. 5 whichare identical to those shown in FIG. 1 are denoted by identicalreference characters.

Base station apparatus 40 comprises antenna 11 for receiving atransmission signal that has been spread according to the CDMA schemefrom a mobile terminal on a transmission side, not shown, and receiver12 having an interface function for a signal received by antenna 11 anddemodulating the reception signal. Base station apparatus 40 alsocomprises parameter manager 41 for allotting inherent spreading codes torespective communication channels (CH) and managing the spreading codes,N searchers 42 ₁ to 42 _(N) and N fingers 43 ₁ to 43 _(N) for beingallotted to the respective communication channels by parameter manager41, reception processor 16 for performing a predetermined receptionprocess on the reception signal over certain paths extracted by fingers43 ₁ to 43 _(N), and interpolation position controller 44 for changinginterpolation positions of interpolating processes upon path searchingin the searchers.

N searchers 42 ₁ to 42 _(N) are structurally identical to each other.Here, an arrangement of first searcher 42 ₁ will be described below.

As shown in FIG. 5, first searcher 42 ₁ comprises code generator 45,path search processor 46, path controller 47, and interpolating filter48. Code generator 45 generates a spreading code for the communicationchannel allotted by parameter manager 41. Path search processor 46 hascorrelation value calculator 21, in-phase adder 22, and power adder 23.

N finger 43 ₁ to 43 _(N) are structurally identical to each other. Here,an arrangement of first finger 43 ₁ will be described below.

First finger 43 ₁ comprises code generator 52 for generating a spreadingcode for the communication channel allotted by parameter manager 41, adespreader 53 for extracting a particular path corresponding to a delaytime indicated by first searcher 42 ₁ from a demodulated signal fromreceiver 12 and despreading the signal from the extracted path with thespreading code generated by code generator 52, a detector 54 forperforming channel estimation and removing the effect of fading, and aRAKE combiner 55 for combining detected signals.

Details of searchers 42 ₁ to 42 _(N) and fingers 43 ₁ to 43 _(N), asexemplified by first searcher 42 ₁ and first finger 43 ₁ will bedescribed below.

First searcher 42 ₁ is supplied with an interpolation position controlsignal from interpolation position controller 44. According to theinterpolation position control signal, first searcher 42 ₁ allowsinterpolating filter 48 to perform an interpolating operation betweenvarious processing operations in path search processor 46. Interpolatingfilter 48 has been provided with interpolating filters corresponding toa plurality of oversampling numbers. Interpolating filter 48 is capableof performing interpolation operation at a plurality of chip intervalswhen the oversampling number is changed by the interpolation positioncontrol signal. Alternatively, interpolating filter 48 may employ thestructure shown in FIG. 3 where the oversampling number is “2” and thetap length is “4”, and may be looped twice to perform an interpolationprocess where the oversampling number is “4”, for example, with an easyand simple arrangement.

Path controller 47 detects a peak in excess of a predetermined thresholdfrom a delay profile that has been generated as a result of a pathsearching process in path search processor 46 where an interpolationprocess is inserted depending on an interpolation position controlsignal, and indicates a delay time corresponding to the detected peak tofirst finger 43 ₁.

In the present embodiment, a non-illustrated mobile terminal on atransmission side sends a framed transmission signal having a pluralityof time slots. The transmission signal is received by base stationapparatus 40. To each of the time slots, there is added a pilot signalat its leading position which represents a fixed pattern known to bothtransmission and reception sides. The pilot signal isquadrature-modulated together with the transmission data and thereafterspread over a spectrum using a spreading code inherent in eachcommunication channel. Transmission signals that have been spread usingrespective inherent spreading codes according to the CDMA scheme arereceived at antenna 11. Receiver 12 performs signal interface conversionsuch as amplification and quadrature demodulation. Here, the signalinterface conversion is conversion such as multiplication of a receptionsignal by a reference frequency which is generated by a referencefrequency generator, not shown, with a multiplier to convert thereception signal into a baseband signal.

Parameter manager 41 is capable of allotting the reception signal tofingers 43 ₁ to 43 _(N) and searchers 42 ₁ to 42 _(N) for respectivecommunication channels included in the reception signal. For example,parameter manager 41 allots unused fingers and searchers, successivelyfrom first finger 43 ₁ and first searcher 42 ₁, to the reception signal.Then, parameter manager 41 indicates code generating information forgenerating corresponding spreading codes to the allotted fingers andsearchers. The fingers and searchers are constructed such that theygenerate spreading codes that are associated with the code generatinginformation indicated thereto.

Demodulated signals demodulated by receiver 12 are supplied to those ofN searchers 42 ₁ to 42 _(N) which have been allotted by parametermanager 41 and those of N fingers 43 ₁ to 43 _(N) which have beenallotted by parameter manager 41.

Interpolation position controller 44 refers to code generatinginformation indicated by parameter manager 41 to recognize the number ofcommunication channels. Interpolation information which representswhether an interpolation process is to be inserted or not and theoversampling number at the time when an interpolation process is to beinserted has been stored in interpolation position controller 44 hasregistered corresponding to the recognized number of communicationchannels. Interpolation position controller 44 outputs the interpolationinformation corresponding to the recognized number of communicationchannels as interpolation position indicating information to eachcommunication channel portion.

First searcher 42 ₁ interpolates sampling points in order to reduce chipintervals of the reception signal, and generates a delay profile basedon a pilot signal added to the leading position of each time slot of theinterpolated signal. In the delay profile, the power values of receptionsignal components which are orthogonal to each other that aredemodulated by receiver 12 are calculated for respective delay times.Usually, the power values calculated for the respective delay times onthe delay profile represent peaks on a plurality of differentpropagating paths due to multipath fading. First searcher 42 ₁ thendetects peaks in excess of a predetermined threshold, and indicatesdelay times corresponding to the respective detected peaks to firstfinger 43 ₁ associated with first searcher 42 ₁. First finger 43 ₁ thenextracts paths of received waves corresponding to the indicated delaytimes from the demodulated signals demodulated by receiver 12. Theseextracted paths are then estimated for channels by detector 54 forremoval of the effect of fading to a certain extent, and areRAKE-combined and then subjected to a predetermined reception processingin reception processor 16.

FIG. 6 schematically shows an arrangement of an essential portion offirst searcher 42 ₁ and interpolation position controller 44 whichcorrespond to the path searching apparatus according to the firstembodiment of the present invention. Path search processor 46 of firstsearcher 42 ₁ comprises code generator 45 for generating a spreadingcode for a communication channel allotted to first searcher 42 ₁,correlation value calculator 21, in-phase adder 22, and power adder 23.The searcher according to the present embodiment resides in that it canselect whether an interpolation process performed by interpolatingfilter 48 is to be inserted between various processors of path searchprocessor 46 or not, based on interpolation position indicatinginformation indicated from interpolation position controller 44. Toperform the above function, each searcher has four selectors 61 to 64.Interpolating filter 48 comprises four filters 65 to 68 depending on thedetails of its interpolation process.

While interpolating filter 48 inserted in a path searching processcomprises four filters 65 to 68 that are selectively used depending onthe details of its interpolation process in the illustrated embodiment,one filter may be used as interpolating filter 48 in each process. Atany rate, any filter may desirably be arranged within interpolatingfilter 48 insofar as it can perform an interpolation process betweenvarious processes depending on the interpolation position indicatinginformation.

First selector 61 is supplied with a demodulated signal demodulated byreceiver 12 and an output signal from first filter 65 which has beeninterpolated to reduce the chip interval of the demodulated signal, andalternatively selects one of the supplied signals based on theinterpolation position indicating information, as a first selectedoutput signal that is supplied to correlation value calculator 21.

Second selector 62 is supplied with a correlation value calculated bycorrelation value calculator 21 and an output signal from second filter66 which has been interpolated to reduce the chip interval of thecorrelation value calculated by correlation value calculator 21, andalternatively selects one of the supplied signals based on theinterpolation position indicating information, as a second selectedoutput signal that is supplied to in-phase adder 22.

Third selector 63 is supplied with an in-phase addition resultcalculated by in-phase adder 22 and an output signal from third filter67 which has been interpolated to reduce the chip interval of thein-phase addition result calculated by in-phase adder 22, andalternatively selects one of the supplied signals based on theinterpolation position indicating information, as a third selectedoutput signal that is supplied to power adder 23.

Fourth selector 64 is supplied with a power addition result calculatedby power adder 23 and an output signal from fourth filter 68 which hasbeen interpolated to reduce the chip interval of the power additionresult calculated by power adder 23, and alternatively selects one ofthe supplied signals based on the interpolation position indicatinginformation, as a fourth selected output signal that is supplied to pathcontroller 47.

Correlation value calculator 21 detects pilot signals added to theleading positions of respective time slots of the input signal, andcalculates a correlation value between the detected pilot signal and anideal reception signal which are produced by multiplying and spreading aspreading code generated by code generator 45 and a predetermined pilotsignal. In-phase adder 22 performs a certain number of in-phaseadditions “I+I”, “Q+Q” on an I signal and a Q signal, which are signalcomponents orthogonal to each other, of the quadrature-demodulated pilotsignal. Power adder 23 performs a certain number of power additions“I²+Q²” on the signal components that have been added in phase.

Interpolation position controller 44 for outputting interpolationposition indicating information comprises interpolation informationmemory 56 for storing the above interpolation information andnumber-of-communication-channel measuring unit 57 for measuring thenumber of communication channels to be processed based on the codegenerating information indicated by parameter manager 41. Here,number-of-communication-channel measuring unit 57 recognizes the numberof communication channels to be processed from the code generatinginformation indicated by parameter manager 41. However,number-of-communication-channel measuring unit 57 may recognize thenumber of communication channels from a despread signal which isproduced by despreading a reception signal. In this case, whendespreading is performed by using a spreading code other than thecorresponding communication channel, the reception signal becomes almost“0” due to its orthogonal nature. Therefore, when a despread signalwhose level is higher than a predetermined level is obtained for acommunication channel, the communication channel can be recognized as acommunication channel to be processed and it is possible to recognizedthe number of channels to be processed at respective time points.Interpolation information memory 56 stores interpolation informationwhich comprises interpolation position specifying information 58indicating whether an interpolation process is to be inserted or not andan oversampling number 59 at the time an interpolation process is to beinserted, the interpolation information corresponding to the number ofchannels measured by number-of-communication-channel measuring unit 57.

FIG. 7 shows an example of interpolation information stored ininterpolation information memory 56. In the interpolation information,interpolation position specifying information 58 indicating whether aninterpolation process is to be inserted or not and an oversamplingnumber 59 at the time an interpolation process is to be inserted isregistered, corresponding to the number of the communication channels(CH), for each of before and after the process of calculating acorrelation value, the process of performing an in-phase addition, andthe process of performing a power addition, which are carried out bypath search processor 46.

For example, when the number of channels to be processed which ismeasured by number-of-communication-channel measuring unit 57 is “1”,before a correlation value is calculated and before an in-phase additionis performed with the corresponding interpolation position specifyinginformation of “interpolation”, interpolation information for performingan interpolation process with the oversampling number “2” is searchedfor. Similarly, when the number of channels to be processed which ismeasured by number-of-communication-channel measuring unit 57 is “2”,before a correlation value is calculated and after an in-phase additionis performed with the corresponding interpolation position specifyinginformation of “interpolation”, interpolation information for performingan interpolation process with the oversampling number “2” is searchedfor. When the number of channels to be processed which is measured bynumber-of-communication-channel measuring unit 57 is “3”, before acorrelation value is calculated and after a power addition is performedwith the corresponding interpolation position specifying information of“interpolation”, interpolation information for performing aninterpolation process with the oversampling number “2” is searched for.As the number of communication channels to be processed is smaller, aninterpolation process is thus performed as a pre-process to increase thenumber of interpolation processes for thereby increasing the accuracyfor path detection when an extra amount of calculation is available.

The interpolation information searched for based on the number ofchannels to be processed which has been measured bynumber-of-communication-channel measuring unit 57 is indicated, as theinterpolation position specifying information which is represented by acontrol signal having a certain format, to searchers 42 ₁ to 42 _(N).Though the interpolation position specifying information is illustratedas being indicated to only first searcher 42 ₁ in the described whichfollows, it is actually indicated to a plurality of searchers dependingon the reception signal.

FIG. 8 shows an example of a format structure of such interpolationposition indicating information. Specifically, the interpolationposition indicating information which is indicated to first searcher 42₁ is indicated as control information indicating, as a unit,interpolation position 61 where the interpolation position specifyinginformation is “interpolation” and oversampling number 62 correspondingthereto. If there are a plurality of pieces of interpolation positionspecifying information which are “interpolation”, then as many pieces ofinterpolation position indicating information as the number of pieces ofinterpolation position specifying information are indicated to firstsearcher 42 ₁. For example, when the number of channels to be processedis “1”, then two pieces of interpolation position indicating informationindicating that the interpolation position is “before correlation valuecalculation” and the oversampling number is “2” and that theinterpolation position is “before in-phase addition” and theoversampling number is “2” are indicated to first searcher 42 ₁.

First searcher 42 ₁ which selects the insertion of an interpolationprocess into various operation processors in path search processor 46based on the interpolation position indicating information indicated inthe above format has a CPU, not shown, and performs various controlprocesses based on a control program that is stored in a given memorysuch as a ROM or the like.

FIG. 9 schematically shows the content of the processing of a controlprogram that is stored in such a given memory. First searcher 42 ₁ firstrefers to the interpolation position indicating information in theformat shown in FIG. 8 which is indicated from interpolation positioncontroller 44 to determine whether there is an interpolation positionbefore a correlation value is calculated in step S70. If theinterpolation position is “before correlation value calculation”, theninterpolating filter 48 having the structure shown in FIG. 3interpolates a demodulated signal supplied from receiver 12 to reducethe chip interval thereof in step S71. To do so, the oversampling numbermay be set to “2”, in the interpolating filter having the structureshown in FIG. 3.

If the interpolation position is not “before correlation valuecalculation” in step S70, or after performing the interpolationcalculation in step S71, correlation value calculator 21 calculatescorrelation values of pilot signals which are added to the leadingpositions of respective time slots and which are of a predeterminedfixed pattern, of I and Q signal components that have beenquadrature-demodulated and despread. Since the pilot signals are of afixed pattern, they can be determined with accuracy as an idealreception signal in the reception side. In correlation value calculator21, a correlation value with respect to an ideal reception signalgenerated from the pilot signal is calculated for each of the time slotsof the received frame. As the correlation value is higher, the pilotsignal at the leading position of each time slot is closer to an idealwaveform, indicating a better reception sensitivity.

Next in step S73, first searcher 42 ₁ refers to the interpolationposition indicating information indicated from interpolation positioncontroller 44 to determine whether the interpolation position is “beforein-phase addition” or not. If the interpolation position is “beforein-phase addition”, then interpolating filter 48 interpolates thecalculated correlation value to reduce the chip interval thereof in stepS74, as with step S71.

If the interpolation position is not “before in-phase addition” in stepS73, or after performing interpolating operation in step S74, in-phaseadder 22 adds signal components for the respective I and Q signalcomponents for a given number of times N in step S75. Thus, noisecomponents contained in the I and Q signals are removed. The greater thenumber of in-phase additions, the smaller the noise in each of thesignal components.

Next, in step S76, first searcher 42 ₁ refers to the interpolationposition indicating information indicated from interpolation positioncontroller 44 to determine whether the interpolation position is “afterin-phase addition is finished” or not. If the interpolation position is“after in-phase addition is finished”, then interpolating filter 48interpolates the calculated correlation value to reduce the chipinterval thereof in step S77, as with step S71.

If the interpolation position is not “after in-phase addition isfinished” in step S76, or after performing interpolating operation instep S77, power adder 23 adds power values for a given number of times Min step S78. The power values are thus averaged with respect to time,preventing paths from being detected with wrong power values due toinstantaneous noise.

Next, in step S79, first searcher 42 ₁ refers to the interpolationposition indicating information indicated from interpolation positioncontroller 44 to determine whether the interpolation position is “afterpower addition is finished” or not. If the interpolation position is“after power addition is finished”, then interpolating filter 48interpolates the calculated correlation value to reduce the chipinterval thereof in step S80, as with step S71.

In the interpolation position is not “after power addition is finished”in step S79, and/or when the interpolating calculation has beenperformed in step S80, the calculated power value becomes a delayprofile indicating the reception signal that is converted into powervalues for respective delay times in a time series. Then, in step S81,path controller 47 detects a peak in excess of a predetermined thresholdwith respect to the power value for each delay time, and indicates adelay time corresponding to a peak in excess of the threshold to firstfinger 43 ₁. Thereafter, the processing sequence is put to an end.

As described above, the path searching apparatus according to the firstembodiment has interpolation position controller 44 which has storedinformation indicative of whether an interpolation process required toincrease the detection accuracy for a path search depending on thenumber of communication channels to be processed is to be inserted ornot, and oversampling numbers at the time an interpolation process is tobe inserted. The path searching apparatus can change whether aninterpolation process performed by interpolating filter 48 is to beinserted between various processors of path search processor 46 or not,based on interpolation information searched for depending on the numberof channels to be processed which has been measured bynumber-of-communication-channel measuring unit 57. The interpolationinformation is established such that as the number of communicationchannels to be processed is smaller, an interpolation process isperformed as a pre-process to increase the number of interpolationprocesses.

Consequently, it is possible to solve the conventional problem of aminimum accuracy for path detection which is achieved because aninterpolation process has been performed in a fixed processing positionregardless of the number of channels to be processed even if the numberof communication channels is small and an extra amount of calculationavailable. The present embodiment can maintain a maximum amount ofcalculation depending on the number of channels to be processed forincreasing the accuracy for path detection as much as possible whenthere is an extra amount of calculation available.

SECOND EMBODIMENT

The path searching apparatus according to the first embodiment insertsan interpolation process in a processing position depending on thenumber of communication channels during a path searching process,uniformly for each communication channel. On the contrary, according toa second embodiment, a path searching apparatus measures the quality ofa reception signal in each communication channel and changes aninterpolation position for a communication channel whose receptionquality is low for thereby increasing the accuracy for path detection.The constitution of a base station apparatus to which the path searchingapparatus according to the second embodiment is applicable is similar tothat in the first embodiment. Therefore, the second embodiment will bedescribed below mainly with respect to the constitution of a searcherand an interpolation position controller.

FIG. 10 schematically shows an arrangement of an essential portion of asearcher and a interpolation position controller which are the pathsearching apparatus according to the second embodiment. Here, the pathsearching apparatus has searcher 90, interpolation position controller91, and reception quality measuring unit 92. If the path searchingapparatus is applied to the base station apparatus in a mobilecommunication system of the CDMA scheme shown in FIG. 5, then searcher90 corresponds to each of N searchers 42 ₁ to 42 _(N) shown in FIG. 5and interpolation position controller 91 corresponds to interpolationposition controller 44 shown in FIG. 5. Reception quality measuring unit92 is provided in the base station apparatus for being shared by thesearchers.

Reception quality measuring unit 92 is supplied withsignal-to-interference ratio (SIR) values 94 calculated by RAKEcombiners of the respective searchers and monitors reception qualitiesin respective communication channels. Furthermore, reception qualitymeasuring unit 92 determines the reception quality level of a receptionquality which is calculated by comparison with a plurality ofpredetermined thresholds, and indicates the reception quality level of acommunication channel which is lower than a certain reception qualitylevel and a communication channel number for identifying thecommunication channel, to interpolation position controller 91.

Interpolation position controller 91 has interpolation informationcorresponding to a plurality of reception quality levels in addition tothe interpolation information shown in FIG. 7. In the interpolationinformation corresponding to the reception quality levels, interpolationposition specifying information indicating whether an interpolationprocess is to be inserted or not between various processes during a pathsearching process shown in FIG. 7, and an oversampling number at thetime an interpolation process is performed has been stored in advance.Interpolation position controller 91 is supplied with the number ofcommunication channels 95 to be processed from parameter manager 41 andalso specified with communication channels whose reception qualitylevels are lower than a predetermined level from reception qualitymeasuring unit 92. Interpolation position controller 91 searches forinterpolation information depending on the number of communicationchannels which has been measured by the number-of-communication-channelmeasuring unit. With respect to a communication channel whose receptionquality is low which has been indicated from reception quality measuringunit 92, interpolation position controller 91 indicates interpolationinformation depending on the reception quality level, rather than theinterpolation information searched for depending on the number ofcommunication channels which has been measured by thenumber-of-communication-channel measuring unit, as interpolationposition indicating information to the searchers in the respectivecommunication channels. Based on thus indicated interpolation positionindicating information, searcher 90 performs interpolating operation ondemodulated signal 96 at an optimum position, and indicates a receptiontime instant to the finger.

FIG. 11 shows an example of the interpolation position indicatinginformation indicated from the interpolation position controller.Interpolation position indicating information 97 is indicated as controlinformation comprising, as a unit, interpolation position 99 whereinterpolation information specifying information is “interpolation”, andcorresponding oversampling number 100, wherein communication channelnumber 98 for identifying a communication channel is added to theleading portion.

Searcher 90 has, in addition to the arrangement of first searcher 42 ₁shown in FIG. 6, a determining unit for determining whether theinterpolation position indicating information indicated in the formatshown in FIG. 11 is addressed to itself or not. The determining unitdetermines the destination of the received interpolation positionindicating information by comparing it with a communication channelnumber allotted in advance to its own searcher. If the receivedinterpolation position indicating information is determined as beinginterpolation position indicating information addressed to itself, thendetermining unit inserts an interpolation process between variousprocesses during a path searching process depending on the interpolationposition and the oversampling number which are included in theinterpolation position indicating information.

As described above, the path searching apparatus according to the secondembodiment changes the position where an interpolation process isinserted during a path searching process, depending on not only thenumber of communication channels to be processed but also the receptionquality level. Therefore, for a communication channel whose receptionquality level is low, an interpolation process is inserted at a positionfor more interpolation processes so as to be able to carry out anaccurate control process to achieve an increase in the accuracy for pathdetection.

In each of the above embodiments, the position for performing aninterpolation process is changed. However, the present invention is notlimited to such processing details. In the above embodiments,correlation value calculations, in-phase additions, and power additionsare performed as a path searching process. However, the presentinvention is not limited to such processing details.

In each of the above embodiments, the interpolation position is changeddepending on the communication channel. However, the present inventionis not limited to such processing details. In view of the fact that oneuser may possibly use a plurality of communication channels, theinterpolation position may be changed depending on the number of users.

In the above embodiments, the interpolation information is composed ofthe interpolation position specifying information and the oversamplingnumber. However, the present invention is not limited to such processingdetails. For example, by setting the oversampling number to “2”, inadvance with the interpolating filter, the interpolation informationmemory may store only interpolation position specifying information foreach communication channel or each reception quality level.

INDUSTRIAL APPLICABILITY

According to the present invention, as described above, the position forperforming an interpolation process to increase the accuracy of a delayprofile depending on the number of communication channels to beprocessed is changed to detect a path with optimum accuracy depending ona reception processing situation.

The insertion of an interpolation process may be selected before andafter correlation value calculation, in-phase addition, and poweraddition for the generation of the delay profile. Therefore, in view ofa trade-off between an increase in the amount of calculation due to theinsertion of an interpolation process and an accuracy for pathdetection, the amount of calculation and the accuracy for path detectioncan be set to optimum values depending on the number of communicationchannels to be processed, making it possible to effectively utilizevarious resources of the apparatus.

An interpolation process for generating a delay profile is inserted at aposition depending on the reception quality of each communicationchannel that has actually been measured, so that the position forperforming an interpolation process can accurately be controlled foreach communication channel, and the accuracy for path detection can beincreased more flexibly depending on the reception quality.

The oversampling number for specifying a chip interval is included ininterpolation information for controlling a finer interpolation process.

By increasing the number of interpolation processes when the amount ofprocessing to be calculated is smaller, the accuracy for path detectioncan be increased by an extra calculation capability when the number ofcommunication channels is small.

1. A method of searching for a path, comprising: a first interpolatingstep of interpolating a demodulated signal to generate a firstinterpolated signal; a first selecting step of generating a firstselected signal by alternatively selecting said first interpolatedsignal or said demodulated signal based on interpolation information,said interpolation information indicating whether an interpolationprocess for reducing a chip interval is to be performed or not betweenprocesses for generating a delay profile which indicates a temporalchange of reception time instants of said demodulated signal due tomultipath fading; a correlation value calculating step of calculating acorrelation value between a pilot pattern which is included in saidfirst selected signal and has a predetermined fixed pattern and apredetermined expected value; a second interpolating step ofinterpolating the correlation value calculated in said correlation valuecalculating step to generate a second interpolated signal; a secondselecting step of generating a second selected signal by alternativelyselecting said second interpolated signal and said correlation valuebased on said interpolation information; an in-phase adding step ofadding in-phase components of said second selected signal for apredetermined number of times; a third interpolating step ofinterpolating an in-phase addition sum calculated in said in-phaseadding step to generate a third interpolated signal; a third selectingstep of generating a third selected signal by alternatively selectingsaid third interpolated signal or said in-phase addition sum based onsaid interpolation information; a power adding step of adding powervalues calculated from signal components of said third selected signalfor a predetermined number of times; a fourth interpolating step ofinterpolating a power addition sum calculated in said power adding stepto generate a fourth interpolated signal; a fourth selecting step ofgenerating a fourth selected signal by alternatively selecting saidfourth interpolated signal or said power addition sum based on saidinterpolation information; and a path detecting step of detecting a pathin excess of a predetermined threshold based on said fourth selectedsignal.
 2. A method of searching for a path according to claim 1,wherein said interpolation information comprises information indicativeof whether said interpolation process is to be performed or not,depending on the number of communication channels to be processed.
 3. Amethod of searching for a path according to claim 1, wherein saidinterpolation information comprises information indicative of whethersaid interpolation process is to be performed or not, depending onreception quality measured in each communication channel of saiddemodulated signal.
 4. A method of searching for a path according toclaim 1, wherein said interpolation information comprises informationindicative of whether said interpolation process is to be performed ornot, depending on the number of communication channels to be processedand reception quality measured in each communication channel of saiddemodulated signal.
 5. A method of searching for a path according toclaim 1, wherein said demodulated signal comprises a signal produced byconverting a reception signal of a CDMA (Code Division Multiple Access)system into a baseband signal and processing the baseband signal by wayof quadrature demodulation.
 6. An apparatus for searching for a path,comprising: path searching means for generating a delay profile based ona pilot signal which is included in each time slot and has a fixedpattern, according to a path searching process composed of a pluralityof processing units, said delay profile indicating a temporal change ofreception time instants due to multipath fading of a demodulated signal;interpolation information storage means for storing interpolationinformation which indicates whether an interpolation process forreducing a chip interval is to be performed or not before and after eachof the processing units; interpolation position processing control meansfor enabling said path searching means to perform an interpolationprocess before and after each of the processing units based on saidinterpolation information; and path detecting means for detecting areception path based on the delay profile generated by said pathsearching means.
 7. An apparatus for searching a path according to claim6, wherein said interpolation information comprises informationindicative of whether the interpolation process for reducing a chipinterval is to be performed or not, depending on the number ofcommunication channels to be processed.
 8. An apparatus for searching apath according to claim 6, wherein said interpolation informationcomprises information indicative of whether the interpolation processfor reducing a chip interval is to be performed or not, depending on thereception quality measured in each communication channel of saiddemodulated signal.
 9. An apparatus for searching a path according toclaim 6, wherein said interpolation information comprises informationindicative of whether said interpolation process is to be performed ornot, depending on the number of communication channels to be processedand the reception quality measured in each communication channel of saiddemodulated signal.
 10. An apparatus for searching for a path,comprising: interpolation information storage means for storinginterpolation information indicative of whether an interpolation processfor reducing a chip interval between processes for generating a delayprofile is to be performed or not, said delay profile indicating atemporal change of reception time instants of a demodulated signal dueto multipath fading; first interpolating means for interpolating saiddemodulated signal to generate a first interpolated signal; firstselecting means for generating a first selected signal by alternativelyselecting said first interpolated signal or said demodulated signalbased on said interpolation information; correlation value calculatingmeans for calculating a correlation value between a pilot pattern whichis included in said first selected signal and has a predetermined fixedpattern and a predetermined expected value; second interpolating meansfor interpolating the corrected value calculated by said correlationvalue calculating means to generate a second interpolated signal; secondselecting means for generating a second selected signal by alternativelyselecting said second interpolated signal and said correlation valuebased on said interpolation information; in-phase adding means foradding in-phase components of said second selected signal for apredetermined number of times; third interpolating means forinterpolating an in-phase addition sum calculated by said in-phaseadding means to generate a third interpolated signal; third selectingmeans for generating a third selected signal by alternatively selectingsaid third interpolated signal or said in-phase addition sum based onsaid interpolation information; power adding means for adding powervalues calculated from signal components of said third selected signalfor a predetermined number of times; fourth interpolating means forinterpolating a power addition sum calculated in said power adding meansto generate a fourth interpolated signal; fourth selecting means forgenerating a fourth selected signal by alternatively selecting saidfourth interpolated signal or said power addition sum based on saidinterpolation information; and path detecting means for detecting a pathin excess of a predetermined threshold based on said fourth selectedsignal.
 11. An apparatus for searching for a path according to claim 10,wherein said interpolation information comprises information indicativeof whether the interpolation process for reducing a chip interval is tobe performed or not, depending on the number of communication channelsto be processed.
 12. An apparatus for searching for a path according toclaim 10, wherein said demodulated signal comprises a signal produced byconverting a reception signal of a CDMA (Code Division Multiple Access)system into a baseband signal and processing the baseband signal by wayof quadrature demodulation.
 13. An apparatus for searching for a pathaccording to claim 10, further comprising reception quality measuringmeans for measuring a reception quality in each communication channel ofsaid demodulated signal, wherein said interpolation informationcomprises information indicative of whether the interpolation processfor reducing a chip interval is to be performed or not, depending on thereception quality measured in each communication channel of saiddemodulated signal.
 14. An apparatus for searching for a path accordingto claim 10, further comprising reception quality measuring means formeasuring a reception quality in each communication channel of saiddemodulated signal, wherein said interpolation information comprisesinformation indicative of whether the interpolation process for reducinga chip interval is to be performed or not, depending on the number ofcommunication channels to be processed and the reception qualitymeasured in each communication channel of said demodulated signal. 15.An apparatus for searching for a path according to claim 10, whereinsaid interpolation information comprises interpolation positionspecifying information indicative of whether the interpolation processfor reducing a chip interval is to be performed or not depending on thenumber of communication channels to be processed between processes forgenerating said delay profile, and an oversampling number, wherein eachof said first to fourth selecting means makes an alternative selectionbased on said interpolation position specifying information, and whereineach of said first to fourth interpolating means performs aninterpolation based on the corresponding oversampling number.
 16. Anapparatus for searching for a path according to claim 11, wherein saidinterpolation information is set to perform the interpolation processbetween processes for achieving more interpolation processes as thenumber of communication channels to be processes is smaller.
 17. Anapparatus for searching for a path according to claim 15, wherein saidinterpolation information is set to perform the interpolation processbetween processes for achieving more interpolation processes as thenumber of communication channels to be processes is smaller.